This invention relates to a long retracting sootblower for boiler cleaning and particularly to one having an indexing lance tube drive system.
Sootblowers are used to project a stream of blowing medium such as water, air or steam against heat transfer surfaces within large scale boilers to cause slag and ash encrustations to be removed. The blowing medium impact produces mechanical and thermal shock which causes these adhering layers to be removed. One general category of sootblowers is known as the long retracting type. These devices have a retractable lance tube which is periodically advanced into and withdrawn from the boiler and is simultaneously rotated such that one or more blowing medium nozzles at the end of the lance tube project jets tracing helical paths.
Many conventional sootblowers, such as the so-called "IK" sootblower manufactured by applicant, include a lost motion device which causes the nozzles to return along a helical path that bisects the helical path of forward travel. This indexing enables surfaces that were not cleaned during extension to be subjected to blowing medium upon retraction. Although the lance tube nozzles trace different helical paths upon extension and retraction, the positions of these helical paths are nonetheless fixed. Heat transfer surfaces continually subjected to impact by blowing medium suffer from erosion and wear. Furthermore, areas lying between the helical paths of the nozzle jets can sometimes escape adequate cleaning. In view of the foregoing, there is a need to provide a long retracting sootblower device having an indexing mechanism which provides a large number of different yet predictable helical paths traced by the lance tube nozzles.
In accordance with this invention, a sootblower is provided having an indexing drive system which displaces the nozzle helical paths slightly upon each sootblower actuation cycle, and thus overcomes the above mentioned disadvantages of prior art designs. The system according to this invention is particularly adapted for sootblowers having a lance tube driving carriage which is advanced and retracted and simultaneously rotates the lance tube. For many long retracting sootblower designs, the carriage has an electric drive motor which is coupled to a drive train having one or more pinion gears which mesh with elongated gear racks to cause the carriage and the lance tube to be retracted and advanced. The carriage also drives the lance tube for rotation through bevel gears.
In the sootblower of the present invention, an indexing system is provided for the longitudinal advancement of the racks which causes the pinion gear meshing with the rack to advance with respect to the rack upon each actuation cycle. Due to the geared connection between the lance tube longitudinal and rotational drive systems, such drive pinion indexing has the effect of causing a slight change in the position of the helical paths traced by the lance nozzles upon each actuation cycle. The indexing mechanism according to this invention operates automatically and can be incorporated into new sootblowers as well as many existing sootblowers as a retrofit application.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.